!! ABSTRACT Molecular Mechanisms of Copper Transport Copper (Cu) is an essential trace element for growth and development because Cu acts as an indispensable cofactor for a variety of enzymes that are involved in multiple biological processes, and mutations of genes involved in Cu transport result in severe, even lethal, neurodegenerative diseases such as Wilson's disease and Menkes! syndrome. Abnormal Cu levels have also been linked to a range of pathological conditions, including Alzheimer's, Parkinson's, cardiovascular disease and cancer. Despite the overwhelming importance of Cu in health and disease, we have only rudimentary understanding of the molecular basis of Cu transport, with a lack of high-resolution three-dimensional structures and relevant biochemical and biophysical characterization that are essential for the development of appropriate mechanism-based therapeutics. Therefore, our long-term goal is to attain a comprehensive understanding of molecular mechanisms of Cu homeostasis using a combination of biochemical, biophysical, and structural approaches. In cells, appropriate Cu levels are tightly regulated by a sophisticated network of Cu-handling proteins, including Cu transporters, chaperones, and acceptors, to control the acquisition, distribution, and delivery of bioavailable Cu. Ubiquitous in eukaryotes, the copper transporter (Ctr) family of integral membrane proteins, Ctr1 and Ctr2, is involved in Cu transport across cellular membranes including both the plasma and intracellular organelle membranes. We have recently developed innovative methods for large-scale production of Ctr1 and Ctr2 transporter proteins, generation of diffraction-quality crystals, and for successful in vitro reconstitution assays. With these exciting preliminary developments, we are now able to combine X-ray crystallography, in vitro biochemical reconstitution, in vivo functional complementation assays, and site-directed mutagenesis to address Cu transport mechanisms. Specifically, we aim to determine the molecular basis of selectivity and permeation in Cu uptake by Ctr1, the underlying mechanism of zinc regulation in Ctr1, and molecular determinants for Cu transport in Ctr proteins. Our proposed work will provide atomic structures of Ctr1 and Ctr2 transporters in multiple functional states and uncover structural and molecular mechanisms of Cu transport. Detailed understanding of the mechanism, function, and regulation of Ctr proteins will open new therapeutic avenues for the treatment of a broad spectrum of diseases associated with disturbed Cu metabolism.